A cleaning composition useful for cleaning exterior surfaces such as aircraft exterior surfaces and other metal, glass, rubber and polymer surfaces should possess solvent-like properties with respect to greasy soils, and should inhibit corrosion and degradation of metal surfaces. Although a number of commercially available cleaning compositions possess these two properties, few have passed the stringent tests necessary for military specification MIL-PRF-87937D status. To achieve the mil-spec status, a cleaning composition must, in addition to having a de-greasing effect, have a cleaning efficiency of 90% of that of a military control test formula, a corrosion inhibiting effect on metal surfaces outlined in the mil-spec, and a pH of less than 10; be biodegradable; be based on an aqueous and water dilutable formula; form a stable solution or micro-emulsion with water; and remain optically clear and stable at a dilution ratio of 1 to 10 with water. Clarity upon dilution is required because a visual determination of cleaning, for example with respect to an aircraft canopy, is most important in a military application. For ease of transport, the cleaning compound must be a highly dilutable concentrate. MIL-PRF-87937D is incorporated herein by reference, and Table I and Table II of MIL-PRF-87937D are reproduced herein. Independent testing by Scientific Material International Inc. (SMI, Inc.) confirmed the cleaning compound conformed to MIL-PRF-87937D, the overall test results which are reproduced herein as Table 5. More specific, detailed results are provided for the relevant, individual tests (i.e. chemical requirements, physical properties, effect on metals, etc.) at Table 6.
Among aqueous-based cleaning compositions effective as de-greasing agents, lack of clarity upon dilution with water combined with corrosive activity of the composition remain a common, unsolved problem. To be effective as a degreaser, a cleaner may contain an oil or a fatty acid ester. Among the products that have achieved MIL-PRF 87937D status, one product appears to contain an oil additive. However, when such products are diluted according to the mil-spec, the resultant solution is opaque and milky-white.
Thus, a need exists for an aqueous-based, biodegradable, cleaning composition that is effective as a de-greasing agent, anti-corrosive, forms a clear and stable emulsion with water; and remains optically clear and stable at multiple dilution ratios with water.